x, y = 2.5, 2.5

$x_{1}, y_{1}$ = 2, 2

$x_{2}, y_{2}$ = 4, 2

$x_{3}, y_{4}$ = 4, 3

$x_{4}, y_{4}$ = 2, 4

Converting into-local coordinate,

Now, $\phi_{1}=\frac{1}{4}(1-\xi)(1-\eta)$

$\phi_{2} =\frac{1}{4} (1 + \xi)(1 − η)$

$\phi_{3} =\frac{1}{4} (1 + \xi)(1 − η)$

$\phi_{4} =\frac{1}{4} (1 + \xi)(1 − …